diff --git a/api/client/cli.go b/api/client/cli.go
index 44cff0dc46..bb5d191e16 100644
--- a/api/client/cli.go
+++ b/api/client/cli.go
@@ -76,7 +76,7 @@ func NewDockerCli(in io.ReadCloser, out, err io.Writer, proto, addr string, tlsC
 	}
 
 	if in != nil {
-		if file, ok := in.(*os.File); ok {
+		if file, ok := out.(*os.File); ok {
 			terminalFd = file.Fd()
 			isTerminal = term.IsTerminal(terminalFd)
 		}